1320
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
5 CONCLUSION
3D FE analysis can provide useful and valuable information in
geotechnical projects even though robustness and mesh
independency are not yet at the same level than in the 2D
programs.
The embedded pile element seems to give imprecise results
when it is used with standard element mesh. Performance is
clearly improved when the mesh is refined around the pile
element. In that case the results are similar with the volume pile.
This feature slightly reduces calculation performance and
handiness of the element.
Figure 7. Embankment supported with the sheet pile walls.
Overall safety factor of the cross section is traditionally
calculated in LEM so that the slip surface goes under the foot of
the sheet pile wall. Often the adequate safety level is not
reached until the wall is extended deep to the hard soil layers.
Wooden piles can be used to improve embankment stability
if the demanded supporting forces are reasonable. Still, several
piles per track meter should be used, as the mobilized lateral
forces are quite small.
In figure 8 the results from the FEM stability analysis with
the strength reduction method is shown. The initial overall
safety factor is F=1.15. With the sheet pile wall, stability is
improved so that the safety factor is F=1.76. However, the
failure surface is not passing under the wall but through the
wall. In this case the wall is modeled as an elasto-plastic plate
element which bending moment capacity is 426 kNm, which
corresponds a section modulus of w=1200cm
3
. In this case the
failure mechanism includes a structural failure of the sheet pile
wall. It was further observed that also the tensile stress of the
anchors was very close to failure at this safety level.
If sheet pile walls are used to improve embankment stability,
FEA can provide valuable additional information on how
sensitive the structural forces are for the soil strength variation
and what is the real nature of the failure. FEA was found to be a
useful tool for these evaluations as the structural behavior is
also accounted for the analysis. It was shown that the bending
moment and the anchor force can be so sensitive for soil
strength variation that the safety margin can be lower than
expected.
6 ACKNOWLEDGEMENTS
The research work presented in this paper is a part of a Life
Cycle Cost Efficient Track research programme (TERA), which
is conducted by Tampere University of Technology. Research
programme is financially supported by the Finnish Transport
Agency. Their support is gratefully acknowledged.
Figure 8. Failure surfaces from the safety analysis. Initial FOS=1.15
without the reinforcement and FOS=1.76 with the sheet pile wall.
7 REFERENCES
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